TORONTO – The General Services Administration, the U.S. government’s main procurement agency, has begun issuing iPhones alongside BlackBerrys, delivering another knock to Research In Motion’s once-dominant position in Washington.

The GSA, with 12,635 employees, supplies more than $70 billion worth of products and services to other federal agencies a year. GSA staff may now request Apple phones and devices running Google’s Android software if they have applications that can help them work more efficiently with customers such as the Departments of Justice and Homeland Security, said Deborah Ruiz, a GSA spokeswoman. She didn’t say when the change took effect.

The move highlights the challenge facing Thorsten Heins, RIM’s new chief executive officer, who has vowed to rethink the way the company markets and sells BlackBerrys to reverse slumping demand. Sales in the U.S. fell 45 percent last quarter as consumers and businesses opted for iPhones or Android devices for their better Web browsers and wider array of apps.

The U.S. decline is dragging down RIM’s global market share even as sales in emerging markets such as India and Indonesia climb. RIM’s share of the worldwide smartphone market slid to 8.2 percent in the fourth quarter from 14 percent a year earlier, while Apple’s share rose to 24 percent from 16 percent in the same period, according to research firm IDC.

Jamie Ernst, a spokeswoman for RIM, didn’t have any immediate comment.

The sales drop has led to a 90 percent plunge in Waterloo, Ontario-based RIM’s share price from its 2008 high. RIM was trading at just under $15 early last week. Shares of Cupertino, California-based Apple were trading at more than $500 last week.

The National Oceanic and Atmospheric Administration said last week it would support BlackBerrys until May and then begin replacing them with iPhones. Apple’s devices can be integrated into its current infrastructure more cheaply than paying for a dedicated BlackBerry server, said Joe Klimavicz, chief information officer of the weather, ocean and fisheries research agency with 13,000 workers.

Halliburton, the world’s second-largest oilfield-services provider, said this month it will phase out 4,500 BlackBerrys and switch to the iPhone because the Apple device does a better job of supporting internal company applications like software to monitor well construction.

The GSA, which also manages office buildings for more than a million federal employees across the U.S., picks suppliers and negotiates prices for more than 12 million products and services.

The Washington-based agency will continue to issue BlackBerrys alongside other devices and allow employees to choose their own device from an approved list, Ruiz said. The agency has no plans to support employees’ own devices, a policy adopted by some companies seeking to reduce costs. Ruiz didn’t say how many smartphones the GSA issues to employees or what the breakdown is by type of device.